1. The Field of the Invention
Embodiments of the invention relate to methods for making polymeric coatings for use on implantable medical devices. More particularly, embodiments of invention relate to methods for making methacrylate copolymers that include monomers that mimic asparagine or glutamine and the use of these polymers on medical devices.
2. The Related Technology
Implantable medical devices, including stents, can be coated with polymers to give the implantable device beneficial properties when used in living tissue. Implant coatings, particularly stent coatings, typically need to simultaneously fulfill many criteria. Examples of desirable properties for implant coating properties include: adhesion to the implant (e.g., adhesion to stent struts) to prevent delamination; adequate elongation to accommodate implant deformation without buckling or cracking; sufficient hardness to withstand crimping operations without excessive damage; sterilizability; ability to control the release rate of a drug; biocompatibility including hemocompatibility and chronic vascular tissue compatibility; in the case of durable or permanent coatings, the polymer needs to be sufficiently biostable to avoid biocompatibility concerns; processability (e.g., production of stent coatings that are microns thick); reproducible and feasible polymer synthesis; and an adequately defined regulatory path.
Many methacrylate polymers exhibit several of the forgoing properties. However, some desired properties or combinations of desired properties have been difficult to achieve in methacrylate polymers. For example, homopolymers of hydrophobic methacrylates such as PMBA, can have a low permeability for drugs of interest, leading to a slower drug release rate than desired.
Recently, efforts have been made to copolymerize traditional methacrylate monomers with other monomers to achieve a copolymer that has the benefits of known methacrylate homopolymers and overcomes their deficiencies. One challenge to developing novel methacrylate copolymers has been achieving the desired mechanical properties, and controlling the drug release, while maintaining biocompatibility. Good biocompatibility is essential for patient safety, necessary for device efficacy, and important for receiving regulatory approval to use the polymer on an implantable medical device.